The overall aim is to develop and demonstrate a small fiber optic probe that incorporates electrogeneration of chemiluminescence (CL) to be used for determination of trace concentrations in solution; both the luminol and the Ru(bipy)2+3 CL systems will be utilized. Aims to be addressed in turn are: 1) Evaluate positioning the working electrode at a small distance from the fiber optic bundle vs. depositing an optically transparent electrode directly upon the surface of the bundle. 2) Examine use of dissolve CL reagent vs. incorporation of the CL reagent into a thin polymeric film on the surface of the working electrode. 3) Examine consequences of stirring the solution vs. allowing it to remain still. 4) Determine working ranges, detection limits, and precisions for determinations of hydrogen peroxide and luminol (with luminol CL) and determination of oxalate and Ru(bipy)2+3 (with Ru(bipy)2+3 CL). Luminol CL has demonstrated applicability for determination of species that can be converted to an equivalent amount of hydrogen peroxide (e.g. glucose, creatinine, cholesterol, etc.) and for species that can be tagged with luminol as in immunoassay. Ru(bipy)2+3 CL can be used to determine oxidixable species like oxalate and amines and also species tagged with Ru(bipy)2+3 derivatives. Electrogeneration of CL allows one to avoid sample dilution from addition of catalyst, turn the reaction on and off by control of electrode potential, and physically localize CL emission at the working electrode surface. The plan is to "take the measurement to the sample." The sensor could be under 5 mm diameter so could probe a sample in a small vial. One sensor plan would be to use a platinum wire electrode located approximately 1 mm from the end of an optical fiber bundle; a second approach would be to vapor deposit a thin layer of an optically transparent electrode material (tin oxide or gold) onto the polished surface of the fiber optic bundle. The effect of solution pH, electrode potential, CL reagent concentration, dissolved vs. polymer-entrapped CL reagents and still vs. stirred solution will be investigated. For determination of luminol (or luminol-tagged species) dual working electrodes will be used, one to generate the peroxide reagent and one to electrogenerate luminol CL.